Horizontal axis wind machine with multiple rotors

ABSTRACT

A horizontal-shaft wind machine having improved low wind speed performance and greater overall efficiency consists of multiple rotors, wherein each successive rotor is larger in diameter than the previous rotor moving from the most windward rotor to the most leeward rotor. Each rotor may be coupled to a separate concentric shaft, and all rotors may rotate in the same direction with the output shafts of each rotor coupled via an overrunning clutch to a single shaft, the output of which is used to drive the load. Winglets attached to the leading edge and tip of the rotor sails improve low wind startup torque.

BACKGROUND OF THE INVENTION

This invention relates generally to wind machines, and in particular toso-called horizontal-shaft wind machines.

A wind machine is a device for extracting energy from the wind. Atypical horizontal axis wind machine consists of a pivoting platformmounted to the top of a tower. Attached to the pivoting platform is arotor assembly joined to a power transmission system by horizontalshaft. The power transmission system is coupled to a work-performingdevice, for example an electrical generator or pushrod for pumpingwater. Wind machines can generally be divided into two categories:Lift-type and drag-type. Lift-type wind machines use slender airfoilssimilar to airplane propellers, which create lift as the wind passesover the airfoils to rotate the wind machine rotor assembly. As withaircraft propellers, the pitch of the lift-type airfoils must be matchedto the windspeed for maximum efficiency and the pitch typically variesfrom the root of the airfoil to the tip in order to compensate for thedifferent path velocity of the airfoil along the leading edge. Drag-typewind machines use relatively wide sails with large surface areas, whichact to slow the wind striking the sails and convert a portion of thekinetic energy of the wind into rotary motion of the wind machine rotor.Drag-type wind machines typically include a rudder that extends from therear of the wind machine head for aligning the wind machine so that therotor always faces the wind.

Conventional wind machines, be they lift-type or drag-type typicallycomprise a single set of blades or a single rotor rotating about ahorizontal shaft. Theoretically, the aerodynamic efficiency yielded by asingle set of blades or by a single rotor cannot exceed 59.6% (See Betz,A. “Wind-Energie and Ihre Ausnutzun durch Windmuelen,” van den Hoeck &Ruprech, Goettingen, 1926). In practice, the output of typicalsingle-bladed wind machines is substantially below 59.6%.

Multiple-rotor wind machines have been suggested as a solution to thelimited aerodynamic efficiency of single bladed wind machines. U.S. Pat.No. 3,974,396 to Schonball discloses a lift-type windmill having twoaxially-displaced counter-rotating rotors in which one rotor drives thearmature and the other rotor drives the stator of an electricalgenerator. This arrangement of counter-rotating blades enables therelative rotational speed between the armature and stator to bemultiplied.

U.S. Pat. No. 7,384,239 to Wacinski discloses a lift-type windmillhaving two axially-displaced coaxial counter-rotating rotors each havingtwo or more airfoils. The output of the counter-rotating rotors iscombined through a planetary transmission to drive the single inputshaft of an electrical generator.

U.S. Pat. No. 4,065,225 Allison discloses a multiple vane lift-typewindmill having a plurality of axially-displaced rotors each havingblades that are spring loaded to adjust the blade pitch as the rotorspeed increases. The rotors of Allison are attached to a single shaftand do not counter-rotate. None of these patents suggest a drag-typewind machine in which the multiple rotors increase in diameter in adownwind direction, nor do they suggest a drag-type wind machine inwhich the rotors are angled rearward along a conical surface, nor adrag-type wind machine in which the sails have winglets formed on theleading and/or tip edges of the sails.

SUMMARY OF THE INVENTION

The present invention comprises a horizontal wind machine havingimproved low-wind operability. According to one embodiment of thepresent invention, a wind machine comprises a horizontally extendingshaft with sails coupled to the shaft, extending radially outward fromthe shaft for rotating the shaft. Each sail comprises a front surfacefacing the wind and a leading edge that moves through the air as theshaft rotates. A winglet extends outward from the leading edge of eachsail and curls back over the front surface of the sail for improving theefficiency of the wind machine, by capturing wind that would otherwiseslide off the leading edge of the sail.

In another embodiment of the present invention, the sails extend fromthe shaft in a direction that is not in a plane perpendicular to theshaft, but instead the sails are angled backward along a conicalsurface. This configuration will cause wind that strikes the sail andslides along the surface to be caught by the winglets at the ends of therotor blades to impart more force in the direction of rotation, thusimproving the efficiency of the wind machine.

In another embodiment, the wind machine comprises a first rotor coupledto a first shaft and a second rotor coupled to a second shaft, whereinthe second shaft is coaxial with the first shaft. The second shaft iscoupled to the first shaft via an overrunning clutch mechanism, such asa ratchet and pawl, which allows the second shaft to transmit torque tothe first shaft if the second shaft would otherwise rotate faster thanthe first shaft. The coupled rotors produce more torque than aconventional wind machine having only one rotor sail assembly of equalouter diameter. Each rotor sail assembly may have non-planar sailorientations as described above and/or winglets extending from either orboth of the leading edges of the sails or the tips of the sails.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be better understood from a reading of thefollowing detailed description, taken in conjunction with theaccompanying drawing Figs. in which like references designate likeelements and, in which:

FIG. 1 is a front-perspective view of a wind machine incorporatingfeatures of the present invention;

FIG. 2 is a side-view of one of the wind machine rotors shown in theembodiment of FIG. 1;

FIG. 3 is a perspective view of one of the wind machine sails shown inthe embodiment of FIG. 2;

FIG. 4 is a front plan view of the embodiment of FIG. 1;

FIG. 5 is a side view of a the embodiment of FIG. 1;

FIG. 6 is a rear perspective view of the embodiment of FIG. 1 showingdetails of the power transmission system; and

FIG. 7 is a side view of an alternative embodiment of a wind machineincorporating lift-type rotors in lieu of drag-type rotors.

DETAILED DESCRIPTION

The drawing figures are intended to illustrate the general manner ofconstruction and are not necessarily to scale. In the detaileddescription and in the drawing figures specific illustrative examplesare shown and herein described in detail. It should be understood,however, that the drawing figures and detailed description are notintended to limit the invention to the particular form disclosed, butare merely illustrative and intended to teach one of ordinary skill howto make and/or use the invention claimed herein and for setting forththe best mode for carrying out the invention.

With reference to FIGS. 1-6 and in particular FIG. 1, a horizontal windmachine 10 incorporating features of the present invention comprises awind machine head 12 which supports a horizontal shaft 14. Horizontalshaft 14, in turn, supports wind machine rotors 16, 18 and 20. Windmachine head 14 is attached to the vertical support column 22 by athrust bearing (not shown), which enables wind machine head 14 to bealigned so that the rotational axis 24 of shaft 14 can be aligned withthe wind direction. Wind machine 10 further comprises a tail section orrudder 26, which aligns the wind machine head 12 so that rotors 16, 18and 20 face the wind.

Each of rotors 16, 18 and 20 have a plurality of sails 28 attachedsubstantially equidistant from shaft 14 to create a substantiallyrotationally balanced circular rotor. Each of the plurality of sails 28has a root 30, a tip 32, a leading edge 34, and a trailing edge 36.Sails 28 may be of any conventional construction, for example fabric,sheet metal, or ultraviolet-resistant plastic, but in the illustrativeembodiment are formed of galvanized steel sheet. The support structureof rotors 16, 18 and 20 is of conventional design as may be found onprior art drag-type wind machines.

As shown most clearly in FIG. 2, each of sails 28 has a concave frontsurface 38 that faces the wind and a convex back surface 40 that facesaway from the wind. Each of sails 28 further comprises one or morewinglets 42 formed at the tip 32 and/or leading edge 34 of sail 28. Withfurther reference to FIG. 3, each of winglets 42 comprises asubstantially circular or arcuate section 44 that extends in thewindward direction over the front surface of sail 28 and curls back overthe front surface 38 of sail 28. Although not wishing to be held to anyparticular theory of operation, it is believed that without winglets,especially in low-wind conditions, a significant portion of the windactually spills over the leading-edge and tip of a conventional windmachine sail.

Winglets 44 capture the energy of this wind, which would otherwise belost.

The rotor design described herein will improve low wind speed start uptorque. The winglet along the leading edge of the sail will capture someof the wind energy that would otherwise slide off the sail. The wingletat the tip of the sail also captures some wind that would otherwiseslide off the tip. A rotor equipped with winglets will start to rotateand impart meaningful energy to a driveshaft in a lower wind speed thana rotor without winglets. The leading edge winglets and the sail tipwinglets may be used separately or in conjunction, depending on thedesign requirements. If used alone, the tip winglets should wrap aroundto encompass a part of the leading edge near the top end of the sail.

With additional reference to FIG. 4, the tips 32 of sails 28 formingrotor 16 form a circle having an outer diameter d₁. Similarly the tips32 of sails 28 forming rotor 18 form a circle having an outer diameterd₂ and the tips 32 of sails 28 forming rotor 20 form a circle having anouter diameter d₃. The outer diameter d₁ of rotor 16 is smaller than theouter diameter d₂ of rotor 18 and the outer diameter d₂ of rotor 18 issmaller than diameter d₃ of rotor 20. The roots 30 of sails 28 formingrotor 16 also form a circle having an inner diameter d₄. Similarly theroots 30 of sails 28 forming rotor 18 form a circle having an innerdiameter d₅ and the roots 30 of sails 28 forming rotor 20 form a circlehaving an inner diameter d₆. The inner diameter d₄ of rotor 16 issmaller than the inner diameter d₅ of rotor 18 and the inner diameter d₅of rotor 18 is smaller than diameter d₆ of rotor 20. Preferably, theinner diameter d₅ of rotor 18 is equal to the outer diameter d₁ of rotor16 within ±50% of the length of blade 28 (from root 30 to tip 32) andthe inner diameter d₆ of rotor 20 is equal to the outer diameter d₂ ofrotor 18 within ±50% of the length of blade 28.

With reference to FIG. 5, the sails 28 forming rotor 16 do not lie in aplane that is perpendicular to shaft 14. Instead sails 28 forming rotor16 lie along a conical surface tapering downwind at an angle θ₁ measuredperpendicular to shaft 14. Similarly, sails 28 forming rotor 18 liealong a conical surface having an angle θ₂ measured perpendicular toshaft 14 and sails 28 forming rotor 2 lie along a conical surface havingan angle θ₃ measured perpendicular to shaft 14. The angles θ₁, θ₂, andθ₃ may be equal or may be unequal. Preferably the angles θ₁, θ₂, and θ₃are at least 8 degrees and are preferably from 11-25 degrees and mostpreferably are about 15±2 degrees. The conical orientation of the rotorscauses wind that would otherwise slide off the root of the sail insteadto slide toward the tip of the sail, imparting force to the sail surfaceduring the process.

Referring now to FIGS. 5-6, horizontal shaft 14 is made up of threeconcentric shaft members 50, 52 and 54. Shaft members 52 and 54 arehollow tubes. The forward end of shaft member 50 is supported by abearing 56 received within the hollow end of shaft member 52. Shaftmember 52, in turn is supported by a bearing 58 received within thehollow end of shaft member 54. Shaft member 54 is attached to windmachine head by bearings mounted within housings 60 and 62, which areattached to wind machine head 12. The rearward ends of shaft members 50and 52 are supported within shaft members 52 and 54 in a like-manner andtherefore will not be discussed in detail.

As shown most clearly in FIG. 6, shaft members 50, 52 and 54 are coupledtogether by means of overrunning clutches 66 and 68. Overrunning clutch66 allows shaft member 50 to rotate faster than shaft member 52.Overrunning clutch 68 allows shaft member 52 to rotate faster than shaftmember 54. In the illustrative embodiment of FIG. 6, overrunningclutches 66 and 68 comprise ratchets consisting of ratchet wheels 70 and72 together with corresponding ratchet pawls 74 and 76.

As can be determined from an inspection of FIG. 6, if shaft member 52tries to rotate in a counterclockwise direction at a speed that is equalto or faster than the counterclockwise rotation of shaft member 50, thentorque is transmitted from shaft member 52 to shaft member 50 viaoverrunning clutch 66. However, if shaft member 52 rotates at a slowerspeed than shaft member 50, no torque is transmitted between the twoshafts. Overrunning clutch 68 similarly transmits torque from shaftmember 54 to shaft member 52 only if shaft member 54 is trying to turnfaster than shaft member 52.

Wind machine 10 generates more torque than a conventional wind machineof the same size because there are three different sets of sails eachgenerating torque and transmitting that torque to one of the coupledshaft members 50, 52, 54. The coupled shafts then combine the torque andtransmit it to the load via vertical shaft 80 and right-angle drive 78.

With further reference to FIG. 6, because the longitudinal axis 15 ofhorizontal shaft 14 is offset by a distance A from the vertical pivotaxis 82 of wind machine head 12, the force of the wind acting on rotors16, 18 and 20 produces a torque about vertical pivot axis 82. In extremehigh wind conditions, this torque will cause longitudinal axis 15 toswing away from the wind direction thereby preventing an overspeedcondition. As wind machine head 12 swings away from the wind direction,rudder 26 pivots relative to wind machine head 12. Rudder 26 is mountedon a pivot 84 that is canted at an angle ϕ relative to vertical. Thus,as rudder 26 pivots relative to wind machine head 12 rudder 26 swingsupward. The upward motion of rudder 26 generates a restoring torque thatmoves longitudinal axis 15 back into the wind when the extreme high windconditions subside.

Although certain illustrative embodiments and methods have beendisclosed herein, it will be apparent from the foregoing disclosure tothose skilled in the art that variations and modifications of suchembodiments and methods may be made without departing from theinvention. For example, although the illustrative embodiment of FIGS.1-6 contemplates three rotors and three shafts all rotating in the samedirection, two rotors and two shafts rotating in the same directions, orgreater than three rotors and three shafts rotating in the same ordifferent directions are contemplated as being within the scope of theinvention. Further, it should be understand that it is within the scopeof the invention for the multi-rotor wind machine design describedherein to be utilized either separate from or in conjunction with sailshaving winglets. Similarly, although wind machine 10 is shown withoverrunning clutches 66 and 68 comprising ratchet and pawls, otherequivalent overrunning clutches such as ramp-and-ball, sprag-clutches orany other similar coupling means are considered to be equivalents andtherefore within the scope of the invention.

Additionally, as shown in FIG. 7, wind machine 100 incorporatingfeatures of the present invention may incorporate airfoil lift-typerotors 86, 88 and 90 in lieu of the drag-type rotors of the embodimentof FIGS. 1-6. As with the embodiment of FIGS. 1-6, rotors 86, 88 and 90may be of equal outside diameter, but preferably rotors 86, 88 and 90increase in diameter in the downwind direction. This arrangementprevents the upwind rotor(s) from blocking the wind from the downwindrotor(s). Also, as with the embodiment of FIGS. 1-6, rotors 86, 88 and90 are preferably coupled to concentric shafts 50, 52, 54 respectively,which are coupled together by means of overrunning clutches 66 and 68.

Wind machine 10 may be used for AC or DC electric power generation,pumping water, or any other task performed by wind machines andtherefore the invention is not intended to be limited to the manner inwhich the power is transmitted to the ultimate load. Accordingly, it isintended that the invention should be limited only to the extentrequired by the appended claims and the rules and principles ofapplicable law. Additionally, as used herein, unless otherwisespecifically defined, the terms “substantially” or “generally” when usedwith mathematical concepts or measurements mean within ±10 degrees ofangle or within 10 percent of the measurement, whichever is greater.

1-3. (canceled)
 4. A wind machine adapted to extract work from windblowing from a windward direction toward a leeward direction, the windmachine comprising: a rotor shaft having a substantially horizontal axisof rotation; a bearing support capable of aligning the axis of rotationof said rotor shaft with the wind direction; a wind machine rotorrotatable about said rotor shaft, said wind machine rotor comprising ahub attached to said rotor shaft and a plurality of sails attached tosaid hub; each of said plurality of sails comprising a sail having aconcave front surface facing the windward direction, said sail furthercomprising a leading edge, a trailing edge, a root a tip and a wingletthat extends windward of and curls back over the front surface of thesail.
 5. The wind machine of claim 4, wherein: said winglet extends inthe windward direction from the leading edge of said sail.
 6. The windmachine of claim 4, wherein: said winglet extends in the windwarddirection from the tip of said sail.
 7. The wind machine of claim 4,wherein: The winglet has a substantially circular curled portion andextends back over the front surface of said sail a distance of no morethan 10% of the maximum chord width of said sail. 12-19. (canceled) 20.The wind machine of claim 4, wherein: said plurality of sails extendsubstantially radially outward substantially equidistant from said hubalong a conical surface centered around said rotor shaft extending in aleeward direction, said conical surface having a conical angle of atleast 8 degrees relative to a plane extending perpendicular to the axisof rotation of said rotor shaft.